Low toxicity fuel and lubricant for two-stroke engines

ABSTRACT

A low toxicity fuel and lubricant for two-stroke engines includes a fuel component that is based on ethanol and includes 2-25% volatile hydrocarbon fractions, and a lubricant component based on an oil that is soluble in ethanol, for example castor oil.

The present invention relates to a low toxicity fuel and lubricantpackage for two-stroke internal combustion engines and in particular,but not exclusively, for high performance two-stroke engines, forexample for racing and recreational vehicles. The invention also relatesto a lubricant for use as a component of a fuel and lubricant packagefor two-stroke engines.

The two-stroke engine has considerable merit in a wide range ofapplications. These include motor sport (in particular, karting),motocross, outboard engines, mopeds, motor scooters, chainsaws andsnow-mobiles. The advantages include low weight, mechanical simplicity,low cost and low noise as compared to four-stroke engines of a similarpower when used in motorsport applications.

Basic two-stroke engines have emissions that are high in unburned fuel,and when they operate at low power settings these engines will often“four-stroke” as a direct result of inadequate scavenging. This form ofmisfiring will result in substantial proportions of the unburned fuelbeing discharged in the exhaust. These hydrocarbon (HC) emissions aretoxic and cause serious pollution problems.

Gasoline direct injection delivers major improvements in both fuelconsumption and in hydrocarbon emissions, when applied to two-strokeengines. However, engines used in karting and in many other sectors thatuse the two-stroke cycle cannot justify expensive direct injectiontechnologies and still use some form of carburettor. Further, sometwo-stroke engines used in competition operate at over 14,000 rpm and atpresent the application of reliable direct injection technology at suchhigh engine speeds seems impractical.

The real weakness therefore of the basic two-stroke engine, when it isfuelled by carburation and crankcase scavenging, is the high level oftoxic exhaust emissions. The problem results from the fact that some ofthe unburned hydrocarbon fuel manages to escape by “short circuiting”via the open exhaust port during the scavenge phase. This is the periodwhen the products of combustion are leaving the cylinder and the freshcharge of fuel and air is being introduced via the transfer ports.

An objective of the invention is to provide a fuel and lubricant packagethat can reduce the toxicity of the emissions from “basic” two-strokeengines, whenever fuel and lubricant is supplied to the engine as apre-mixed fuel and lubricant package. A further objective is to providea fuel and a lubricant for use with two-stroke engines, where separatesupply tanks are used for the fuel and the lubricant, but where thelubricant is still used on a “total loss” basis. One other objective isto provide a fuel and lubricant package with low toxicity to minimisethe health risks associated with the handling of fuels and lubricants inthe recreational sector.

According to the present invention there is provided a fuel andlubricant for two-stroke engines, including a fuel component that isbased on ethanol and includes 2-25% volatile hydrocarbon fractions, anda lubricant component which is based on an oil that is soluble inethanol.

Because ethanol is relatively non-toxic, the release of unburned fuel inthe exhaust gases does not give rise to significant health risks. Theinclusion of a lubricant that is soluble in ethanol makes the fuel andlubricant mixture suitable for use in two-stroke engines. Although somevolatile hydrocarbon fractions are frequently required for coldstarting, the quantity is sufficiently low to avoid causing significanthealth risks.

Advantageously, the fuel component includes 75-98% ethanol, preferably85-95% ethanol.

Advantageously, the ethanol and hydrocarbon is blended for high octaneand low toxicity.

Advantageously, the fuel component includes 3-15% volatile hydrocarbonfractions.

Advantageously, the volatile hydrocarbon fractions are selected from thegroup comprising pentane, iso-pentane, butane, iso-butane, propane andcombinations thereof. These fractions have low toxicity and appear to bepromising candidates for this application. Any other hydrocarbonoffering low toxicity, good volatility and high octane rating and flamespeed may also be suitable.

Advantageously, the fuel component includes one or more additivesselected from a range that includes corrosion inhibitors, combustionenhancers, solubility aids and cold starting promoters.

Optionally, the fuel component may include 1-20% water, preferably 3-10%water. The inclusion of water reduces the combustion temperature and solowers the production of NOx.

Advantageously, the lubricant component is based on a non-mineral oil.This further reduces the presence of unburned hydrocarbons in theexhaust gases. By the term “based on” we mean that the non-mineral oilcomprises the major part of the oil present in the lubricant: i.e atleast 50%, preferably at least 80%, and more preferably at least 90% ofthe lubricant. In certain circumstances, the lubricant component mayinclude small quantities of other oils.

Advantageously, the lubricant component is based on a vegetable oil oran equivalent low toxicity synthetic oil. Preferably, the lubricantcomponent is based on castor oil. We have found that the combination ofan ethanol based fuel and a castor oil based lubricant is particularlyeffective. Alternatively, the lubricant component may be based on jojobaoil or an equivalent low toxicity synthetic oil.

Advantageously, the lubricant component includes one or more additivesselected from a range that includes corrosion inhibitors, solubilityaids and detergents.

Advantageously, the lubricant component is combined with the fuelcomponent at a rate of 0.5-5.0 cc per 100 cc of the fuel component,preferably at a rate of 1-4 cc per 100 cc of the fuel component.

According to another aspect of the invention there is provided alubricant for use in a fuel and lubricant as defined by any one of thepreceding statements of invention, wherein the lubricant is based on anoil that is soluble in ethanol.

Advantageously, the lubricant is based on a non-hydrocarbon oil,preferably a vegetable oil or an equivalent low toxicity synthetic oil.The lubricant may be based on castor oil or an equivalent low toxicitysynthetic oil. Alternatively, the lubricant may be based on jojoba oilor an equivalent low toxicity synthetic oil.

Advantageously, the lubricant includes one or more additives selectedfrom a range that includes corrosion inhibitors, solubility aids anddetergents.

An objective of the invention is to provide a fuel and lubricant for usein two-stroke engines in applications where very high power is the primerequisite. Such engines generally operate rich of stoichiometric tomaximise power, but as a result high levels of unburned fuel will bepresent in the exhaust gases. Such conditions are commonplace incompetition two-stroke engines. Typically, such engines run at air-fuelratios of around 12.5:1 when using gasoline. As shown in the enclosedgraph (FIG. 1), this results in high levels of exhaust toxins. Anobjective of the invention is therefore to provide a fuel that has lowtoxicity in the exhaust gas. A further objective of the invention is tominimise the health risks associated with use and handling of the fuelwithin the competition and recreational sectors.

Blair (“The Basic Design of Two-Stroke Engines”, Warrendale, Pa.:Society of Automotive Engineers, 1990) conveys a picture of reasonablylow CO, low NOx, but high unburned hydrocarbon emissions in respect of“basic” crankcase scavenged two-stroke engines. This poor emissionpicture relates largely to the discharge of unburned hydrocarbon fuelsand to a lesser extent some of the lubricant. However, this picturechanges completely if an environmentally friendly fuel (a gasolinereplacement) and a benign bio-lubricant are used to replace the bulk ofthe hydrocarbons in the fuel and to replace the synthetic andsemi-synthetic lubricants which are generally toxic. It should also bepossible to create a “synthetic” non-toxic lubricant that is suitablefor two-stroke applications when used with ethanol. Solubility is afundamental requirement which the castor based lubricants appear toalready meet.

Some appropriate hydrocarbons remain useful to improve cold startingcharacteristics, but these are only required in small proportions. Thecorrect hydrocarbons are required for this clean fuel technology, andthere is the need to select hydrocarbon fractions with low toxicity,high octane rating and appropriate volatility as the key blendingrequirements.

The main exhaust gases are carbon-dioxide, nitrogen and water vapour.These gases are relatively benign: however, the worst pollutants in theengine's exhaust are those products of incomplete combustion, namelycarbon-monoxide and a range of unburned hydrocarbons. The oxides ofnitrogen (NOx) are the result of atmospheric nitrogen and oxygen whichwill combine under conditions of high temperature and pressure. However,the emissions of NOx are generally much lower from two-stroke enginesthan from the four-stroke counterparts.

Emissions of carbon-monoxide can be minimised by good combustion chamberdesign and by operating with air-fuel ratios “lean” of stoichiometric(oxygen rich). Formation of NOx can be minimised by any reduction in thepeak combustion temperature, and for this purpose a fuel which canabsorb water can prove beneficial. Added water has the disadvantage thatit will increase the risks of corrosion, but anti-corrosion additivesshould serve to minimise the problems. Materials used in the engine fuelsystem should also be selected to reduce the corrosion problems.

A combination of alternative fuels and lubricants is proposed as asolution to the above emission problems and to reduce the health risksassociated with handling highly toxic fuels and lubricants. The initialblends proposed here provide the opportunity to retain a liquid fuel andto replace the toxic unburned fuels and lubricants which are emitted inthe exhaust gases from “basic” two-stroke engines. Instead thosecomponents which have been specified have been selected for their benignnature, whilst providing the opportunity to maintain or improve octanerating and charge density.

A range of additives is required to address various issues such ascorrosion, solubility, cold starting and a number of undesirablecharacteristics. It may also prove beneficial to improve luminosity ofthe flame with an appropriate marker-tracer. The appropriate additiveswill be incorporated into both the lubricant and the fuel.

Various embodiments of the invention will now be described by way of thefollowing examples.

EXAMPLE 1

Compound Percentage Ethanol 85% Pentane or iso-pentane 15% Plus fueladditive package 100% fuel element Castor Based Oil 03% (i.e. 33:1fuel:lubricant mix) Plus ethanol specific additive package

The fuel and lubricant comprises a combination of an ethanol-based fuelcomponent mixed with a castor based lubricant component. The fuelcomponent comprises approximately 85% ethanol and 15% pentane oriso-pentane, plus a small quantity (typically less than 1% by weight) offuel-specific additives, which may include, for example, corrosioninhibitors, combustion enhancers and aids for cold starting.

The lubricant component consists of castor oil (natural or a lowtoxicity synthetic oil) plus a small quantity of an ethanol-specificadditive package including, for example, corrosion inhibitors, additivesto aid solubility and detergents to minimise the formation of lacquersand varnishes.

The fuel component and the lubricant component may be supplied blendedtogether for immediate use, or they may be supplied separately formixing prior to use. In use, the two components are blended at a fueland lubricant ratio of approximately 33:1, by adding 3 cc of thelubricant component per 100 cc of the fuel component.

EXAMPLE 2

Compound Percentage Ethanol 90% Butane or iso-butane 03% Iso-pentane orpentane 07% Plus fuel additive package 100% fuel element Castor BasedOil 02% (i.e. 50:1 fuel:lubricant mix) Plus ethanol specific additivepackage

The fuel component in this example is similar to that of Example 1,except that the quantity of ethanol has been increased to 90% and thetotal hydrocarbon component has been reduced to 10% (comprising 3%butane or iso-butane and 7% pentane or iso-pentane). The fuel andlubricant components are blended at a ratio of 50:1 (2 cc lubricant per100 cc fuel).

EXAMPLE 3

Compound Percentage Ethanol 95% Propane 01% Butane or Iso-butane 01%Iso-pentane 03% Plus fuel additive package 100% fuel element JojobaBased Oil 02.5% (i.e. 40:1 fuel:lubricant mix) Plus ethanol specificadditive package

In this example, the quantity of ethanol in the fuel component has beenincreased to 95% and the total hydrocarbon component has been reduced to5% (1% propane, 1% butane or iso-butane and 3% iso-pentane). Thelubricant component is based on jojoba oil, plus a suitable additivepackage as in Example 1. The fuel and lubricant components are combinedat a ratio of 40:1 (2.5 cc lubricant per 100 cc of fuel).

EXAMPLE 4

Compound Percentage Ethanol 93% Propane 01% Butane or iso-butane 02%Iso-pentane 04% Plus fuel additive package 100% fuel element CastorBased Oil 02% (i.e. 50:1 fuel:lubricant mix) Plus ethanol specificadditive package

In this example, the fuel component includes 93% ethanol and 7%hydrocarbon (1% propane, 2% butane or iso-butane and 4% iso-pentane).The lubricant is based on castor oil and is combined at a fuel andlubricant ratio of 50:1 (2 cc lubricant to 100 cc of fuel).

EXAMPLE 5

Compound Percentage Ethanol 85% Water 06% Butane or iso-butane 02%Iso-pentane 07% Plus fuel additive package 100% fuel element JojobaBased Oil 03% (i.e. 33:1 fuel:lubricant mix) Plus ethanol specificadditive package

In this example, water is included in the fuel component for lower NOxemission, the fuel component comprising approximately 85% ethanol, 6%water and 9% hydrocarbon (2% butane or iso-butane and 7% iso-pentane),plus additives. The lubricant is based on jojoba oil and is combined ata fuel and lubricant ratio of 33:1 (3 cc lubricant per 100 cc of fuel).

EXAMPLE 6

Compound Percentage Ethanol 85% Butane or iso-butane 02% Iso-pentane 13%Plus fuel additive package 100% fuel element Castor Based Oil 02% (i.e.50:1 fuel:lubricant mix) Plus ethanol specific additive package

In this example, the fuel component includes 85% ethanol and 15%hydrocarbon (2% butane or iso-butane and 13% iso-pentane), plusadditives. The lubricant is a castor based oil and is combined at a fueland lubricant ratio of 50:1 (2 cc lubricant per 100 cc of fuel).

The key to this novel approach to the problems of two-stroke competitionengine emissions is provided by ethanol. However, for two-strokeapplications a lubricant is required which will dissolve readily inethanol. It must burn cleanly and also be benign in the unburned form.Castor oil is a known lubricant and it also behaves as a fuel when it isinjected in a finely atomised form into diesel engines. Castor oildissolves in ethanol and in the combustion chamber it appears to burncleanly, while unburned castor oil in the exhaust gases should bebiodegradable and relatively benign. In contact with the metallicrubbing and bearing surfaces castor oil has been shown to provideexcellent lubrication qualities. A castor based lubricant thereforeappears attractive for these purposes. However, some alternativelubricants may also prove to be appropriate for these applications:these could include vegetable based oils of which jojoba basedlubricants appear to be promising candidates.

An initial formulation to address the two-stroke emission problem ismade up as follows: a lubricant amounting to 1-4% of a castor orvegetable oil: this is mixed into a fuel made up of between 2-20% ofappropriate hydrocarbons which are selected for their low toxicity, goodvolatility, high flame rate and high octane rating. These hydrocarbonsare likely to originate from the “front-end fractions” of the refiningprocess: they can include the heavier hydrocarbon gases and the lighterhydrocarbon liquids. These specific hydrocarbon components will act asthe cold starting aid. The composition of this hydrocarbon fraction willbe varied depending on the application and the ambient temperatureswithin a particular market.

These hydrocarbon components must also be selected for solubility inethanol. They can include hydrocarbons which are gaseous at normaltemperatures such as propane and butane and those which are liquid suchas pentane and iso-pentane. However, certain other hydrocarbons may alsoprove appropriate to meet these requirements, the emphasis being towardslow toxicity and good solubility. The remainder of the fuel is ethanol:this is rated at 108 octane RON (some sources quote octane ratings of112-120 RON for ethanol).

To this blend we can consider adding water up to 10% in order to achievefurther NOx suppression and to avoid spark knock. Tests have indicatedthat water is soluble in the ethanol/hydrocarbon/castor oil blends. Theflame temperature of ethanol is lower than with gasoline and the flameluminosity is also less: this will help suppress the formation of NOx.In any case NOx is not a significant problem with two-stroke engines andthe use of ethanol can be expected to further reduce NOx emissions.Adding water may well limit the formation of NOx further but thetrade-off is likely to be an increase in the risk of corrosion to engineand fuel systems components and the requirement for greater fuel tankcapacity.

It is anticipated that in the first instance a two-strokeethanol/hydrocarbon competition fuel will be created. This will be“designed” for blending with a lubricant package which has beenoptimised for this specific fuel. This fuel and lubricant mix will beused with two-stroke engines which rely upon total-loss lubricationsystems. Each of the components and additives is selected to minimisethe toxic risks associated with fuel handling and to minimise toxicexhaust emissions. Each fuel component is also selected to ensuresolubility and compatibility with ethanol and the lubricant formulation.Ethanol is relied upon primarily to provide clean burn, the requiredhigh octane rating and lower levels of toxins in the unburned fuel inthe engine's exhaust gases.

The ethanol specific bio-lubricants created in line with these proposalsare likely to require a range of additives such as corrosion inhibitors,additives to aid solubility and detergents to minimise the formation oflacquers and varnishes. The ethanol-based fuel needs to be blended withcold starting combustion enhancers, whilst aiming to create two-strokeemissions which have low toxicity. This type of fuel blend is essentialin the absence of low cost, direct injection system for high speed, andlow cost two-stroke engines.

The single cylinder two-stroke engine has considerable advantage overcomparable four-stroke engines, in terms of simplicity, power-weightratio, vibration, durability, noise and harshness. In factinvestigations show that small capacity four-stroke engines are notparticularly fuel efficient, as the frictional losses associated withthe valve gear begin to assume considerable proportions as the cylindersize is reduced. There is also the added friction associated with theadditional inlet and exhaust strokes. This reduces the mechanicalefficiency of the smaller four-stroke engines.

If a two-stroke fuel is made primarily of ethyl alcohol and this ismixed with a lubricant which is largely a castor based oil (or a jojobabased oil) it would seem the emissions of unburned fuel and lubricantwould be largely composed of ethanol and castor oil (or jojoba oil).There are likely to be issues associated with corrosion, solubility andengine starting, all of which can be improved through the use ofsuitable additives to both the fuel and the lubricant. These will needto be developed so that the fuel blend and lubricant package areappropriate for a wide range of engine technologies.

Two-stroke engines generally have low on NOx emissions and theseproposals are likely to enhance those characteristics still further.Ethanol, as a result of its high latent heat of evaporation, creates asignificant reduction in the charge temperature compared with gasoline:this helps to reduce peak temperatures and NOx formation. The highlatent heat of evaporation is invaluable for reducing the chargetemperature and for increasing the charge density. The result is anincrease in power output. The fuel also has a higher octane rating thangasolene karting fuels currently mandated by the FIA-CIK. This willpermit the use of increased compression ratios leading to improvedefficiency.

Two-stroke engines with carburettors can be sensitive to “transientspark knock” which is caused by “light end” octane deficiency. Theoctane rating available with ethanol provides an opportunity to avoidthis undesirable condition. However, the hydrocarbon fraction also needsto be carefully selected to avoid similar “light end” octane deficiency.

The two-stroke piston is exposed to twice the firing pulses of itsfour-stroke counterpart; the exposure of the underside of the piston tolower incoming charge temperatures of the ethanol-based fuel and airmixture will assist in piston cooling. There should be similar benefitsby improving the cooling of the lower parts of the cylinder bore. Thisis likely to prove advantageous with two-stroke engines, which are oftenvulnerable to overheating particularly around the exhaust ports.

Lower maximum and mean flame temperatures have been reported withethanol fuel: this will help in NOx reduction and will reduce the heatload on the piston: this is particularly important with the two-strokecycle. We have noted lower coolant temperatures on test and this isbeneficial for durability and also for the avoidance of “spark knock”.The impact of ethanol on the crankcase scavenged two-stroke engineshould prove beneficial; reducing the temperatures of bottom endbearings is likely to improve durability. In fact it is probable thatreduced temperatures will serve to prolong the use of air cooledtwo-stroke engines in a wide range of applications.

We have already conducted initial “field trials” with some basicformulations of the fuel, with various hydrocarbons plus the lubricant;and these proved successful in a lightly modified engine.

The present invention provides for the creation of a high octane butsignificantly more benign fuel for karting and motocross, in the absenceof proven low cost direct injection systems for these applications.There is also a wide range of other two-stroke engine applications forthese fuel and lubricant formulations, where the basic two-stroke engineremains desirable on grounds of simplicity and cost, where thecarburettor remains both difficult and uneconomic to replace, but wherethe toxicity of the exhaust emissions needs to be urgently addressed.

1. A fuel and lubricant package for two-stroke engines, including a fuelcomponent that is based on ethanol and includes 2-15% volatilehydrocarbon fractions, and a lubricant component based on an oil that issoluble in ethanol, wherein the fuel component includes 85-95% ethanol,the lubricant component is based on a vegetable oil or an equivalentsynthetic oil, the lubricant component is combined with the fuelcomponent at a rate of 1-4 cc per 100 cc of the fuel component, and thefuel and lubricant package has a low toxicity.
 2. A fuel and lubricantpackage according to claim 1, wherein the ethanol and hydrocarbon isblended for high octane and low toxicity.
 3. A fuel and lubricantpackage according to claim 1, wherein the fuel component includes 3-15%volatile hydrocarbon fractions.
 4. A fuel and lubricant packageaccording to claim 1, wherein the volatile hydrocarbon fractions areselected from the group consisting of pentane, iso-pentane, butane,iso-butane, propane and combinations thereof.
 5. A fuel and lubricantpackage according to claim 1, wherein the fuel component includes one ormore additives selected from the group consisting of corrosioninhibitors, combustion enhancers, solubility aids and cold startingpromoters.
 6. A fuel and lubricant package according to claim 1, whereinthe fuel component includes 3-10% water.
 7. A fuel and lubricant packageaccording to claim 1, wherein the lubricant component is based on castoroil.
 8. A fuel and lubricant package according to claim 1, wherein thelubricant component is based on jojoba oil.
 9. A fuel and lubricantpackage according to claim 1, wherein the lubricant component includesone or more additives selected from the group consisting of corrosioninhibitors, solubility aids and detergents.
 10. (canceled)
 11. A fueledengine comprising a two-stroke engine and the fuel and lubricant packageaccording to any one of claims 1 to 9.